STUDY ON STRENGTH OF CONCRETE USING VARIOUS COARSE AGGREGATES, PART-8

CHAPTER − 4

CONCRETE MIX DESIGN

The design of concrete mix is not a simple task on account of the widely varying properties of the constituent materials, the conditions that prevail at the site of work and the conditions that are demanded for a particular work for which the mix is designed. Design of concrete mix requires complete knowledge of the various properties of these constituent materials, the implications in case of change on these conditions at the site, the impact of the properties of plastic concrete on the hardened concrete and the complicated inter-relationship between the variables. All these make the task of mix design more complex and difficult.

Mix design can be defined as the process of selecting suitable ingredients of concrete and determining their relative proportions with the object of producing concrete of certain minimum strength and durability as economically as possible. The purpose of designing as can be seen from the above definitions is two-fold. The first object is to achieve the stipulated minimum strength. The second object is to make the concrete in the most economical manner.

With the given materials, the four variable factors to be considered, in

A Trail Batch for Mix Design

connection with specifying concrete mixes are:

(1) Water-cement ratio

(2) Cement content or cement-aggregate ratio

(3) Gradation of the aggregates

(4) Consistency

In general all four of these inter-related variables can not be chosen or manipulated arbitrarily. Usually two or three factors are specified, and the others are adjusted to give minimum workability and economy.